1. Field of the Invention
The present invention relates to a method for forming a thin-film lithium-ion battery.
2. Discussion of the Related Art
Lithium-ion type batteries have the advantage of comprising a solid non-flammable electrolyte, which further has a good ion conductivity over a wide range of temperatures. Such batteries could advantageously be used in mobile electronic devices such as cell phones or laptop computers.
To form thin-film lithium-ion batteries, typically batteries having dimensions smaller than 2.5×2.5 cm, techniques of sputtering through a shadow mask are commonly used. Such techniques comprise placing a shadow mask above a support or substrate and sputtering, through this mask, the different layers forming the battery.
However, for a large-scale production of thin-film lithium-ion type batteries, the use of shadow masks is relatively expensive. Indeed, for each sputtering involving a mask, the sputtered component also deposits on the mask. Thus, between each use of the mask, the different layers deposited on the mask need to be removed and recycled.
Techniques of battery forming by sputtering through a shadow mask also have the disadvantage of not being adapted to form batteries of smaller dimensions (below a 3-mm side length), due to the occurrence of mask alignment problems for such dimensions. Now, such batteries could advantageously be used as backup batteries to save key data in memories in the occurrence of a failure of a main battery.
To form small lithium-ion type batteries, it could be envisaged to adapt lithography techniques, which are well known and controlled in the field of integrated circuits. However, such techniques are relatively expensive when applied over large substrate surface areas. Further, lithography methods require the use of resins which are removed by wet processings (generally, with solvent-based aqueous mixtures) which would cause chemical reactions with the highly reactive lithium-based battery layers. Such techniques are thus not appropriate for the forming of lithium-ion type batteries.
There thus is a need for a method enabling to form relatively inexpensive and small lithium-ion type batteries in thin film technology, adapted to the presence of the highly reactive materials forming such batteries.